1. Technical Field
The invention relates to devices for capturing harmful volatile organic compounds (VOCs) in fuel vapors and more particularly to a fuel tank cap capable of capturing harmful VOCs in fuel vapors generated in a fuel tank of an automobile.
2. Related Art
Extracted hydrocarbons in a liquid form are referred to as petroleum. Gasoline is a transparent, petroleum-derived liquid that is used primarily as a fuel in internal combustion engines of, for example, automobiles. VOCs in fuel vapors generated in a fuel tank are harmful when breathing into the body. Thus, it is important to recover or capture the harmful vapor prior to releasing into the atmosphere.
Fuel tank system of an automobile is used to store gas. The fuel tank system consists of an independent fuel tank and a fuel tank attached to an engine. The fuel tank has an opening for filling gas (i.e., refueling). Vapor may be generated by evaporation of the gas stored in the fuel tank. A cap is provided on the opening for preventing VOCs in the fuel vapors from escaping the fuel tank.
Vapors can exert pressure on an inner surface of the fuel tank. The pressure can be either expansion pressure or contraction pressure. Specifically, in the example of a fuel tank attached to an automobile engine, gas may quickly turn into vapor when temperature is sufficiently high (i.e., high temperature environment), thereby exerting an expansion pressure on the inner surface of the fuel tank. To the contrary, gas may slowly turn into vapor when temperature is sufficiently low (i.e., low temperature environment) or when gas flows to the engine (i.e., decreasing gas in the fuel tank), thereby exerting a contraction pressure on the inner surface of the fuel tank. Both the expansion and contraction pressures should be limited not to exceed a maximum value by regulation and substantial elimination. Otherwise, the fuel tank may explode if the expansion pressure exceeds the maximum value or the gas flow from the fuel tank to the engine is greatly adversely affected if the contraction pressure exceeds the maximum value.
Conventionally, techniques of regulating both the expansion and contraction pressure involve installing a pressure balance device in the fuel line between the fuel tank and the engine, in the fuel tank, or in the fuel tank cap and the pressure balance device may communicate with the atmosphere.
In the example of installing a pressure balance device, an activated carbon canister is installed in the fuel line between the fuel tank and the engine or installed in the fuel tank in advanced technology. The activated carbon canister is provided in a vapor vent channel which is located between a head space in the fuel tank and the atmosphere. The pressure balance device is implemented as an activated carbon canister can balance internal pressure of the fuel tank and the atmospheric pressure and acts as a vehicle fuel vapor emission control system.
Specifically, in response to internal pressure of the fuel tank greater than the atmospheric pressure (i.e., in the case of being expansion pressure), fuel vapors in the fuel tank may pass through a chamber containing activated carbon canister in the vapor vent channel. The activated carbon canister may capture the VOCs in the fuel tank by absorption. The filtered fuel vapors are less harmful and thus are safe to release into the atmosphere. To the contrary, in response to internal pressure of the fuel tank less than the atmospheric pressure (i.e., in the case of being contraction pressure due to consumption of gas), air may enter the fuel tank via the vapor vent channel to increase pressure in the fuel tank. As a result, a pressure balance inside and outside the fuel tank is reached.
However, there are many dead ends in the conventional activated carbon canister in the vapor vent channel and in turn it may adversely affect harmful vapors absorption by the activated carbon. Moreover, in the case of the activated carbon canister being formed integrally with and inside the fuel tank, manufacturers may increase the size of the chamber for receiving an increased amount of activated carbon in order to increase the absorbability of the harmful vapors. However, it has disadvantages including increasing the size and the manufacturing cost of the fuel tank cap, complicating the construction of the fuel tank cap, lowering convenience in use, and making the product less practicable. Thus, the need for improvement still exists.